Why Human Babies Are Fattest (and Smartest)

Feb. 20, 2004 -- The next time you see a plump baby, compliment
the parent on how smart their child will be. A new study shows that baby fat is
linked to the size of babies' heads and future intelligence.

Researchers say human infants have long been recognized as the
fattest newborns, much fatter than other animals that need extra fat for
insulation. In fact, most mammals, including nonhuman primates, don't start
accumulating fat until after birth.

Answering the evolutionary question of why human babies are
born plump has puzzled scientists for years, and many explanations have been
offered. But Portuguese researchers say they now have evidence to back up their
theory.

Fatter Babies Have Bigger Heads

In their study, published in the current issue of the
American Journal of Human Biology, researchers studied 1,069 human
newborns. They found that the fatter the baby was, the bigger his or her head
was likely to be, even after accounting for other factors such as gestational
age and birth length.

They say the finding shows that newborns need that extra fat to
feed their brains during the critical early stages of development.

Previous studies have shown that the brain needs high amounts
of energy in order to function and grow, and the bigger the organ is, the more
energy it needs.

Researchers say this is especially true during infancy when the
brain goes through its maximum growth stage. For example, a newborn's brain can
expend as much as 60% of the total energy produced by the body.

Because human babies are not capable of fending for themselves,
fatness as a newborn may have developed as an evolutionary mechanism to protect
the brain as it develops. Malnutrition in early life can negatively affect the
brain's development and is a major cause of infant death.

Researchers say prior studies have also shown that birth weight
and head size at birth are associated with head size and mental abilities in
childhood and later life. Therefore, newborn fatness would have been favored by
natural selection and explain why the trait has endured throughout human
evolution.